This invention relates to an image processing apparatus and method and, more particularly to an image processing apparatus and method which appropriately controls print processing when an amount of ink to be discharged onto a print medium is limited.
In an ink-jet printing method, an ink-discharge amount acceptable for a print medium (allowable ink-discharge amount) is determined based on the characteristic, e.g., absorptivity, of the print medium. Especially, in case of color printing, if ink-discharge amount exceeds the allowable ink-discharge amount of the print medium, blur occurs at boundaries between respective colors, thus degrading image quality.
Assuming that the amount of ink droplets forming one pixel is 40 p1 (picoliter) per color, the ink-discharge amount per unit area is about 220% with respect to normal paper; about 280% with respect to coated paper; about 300% with respect to an OHP sheet for ink-jet printing; and about 340% with respect to a luster film for ink-jet printing wherein 40 p1 is defined as 100%. In this manner, the allowable ink-discharge amount depends on ink absorptivity of material of print medium.
In consideration of the above situation, a printing technique, which changes the size of ink droplet in accordance with the type of print medium, thus controls ink-discharge amount per unit area, has been proposed.
Further, a printing technique which allows to discharge ink of respective colors as much as possible, within the limitation of ink-discharge amount with respect to a print medium, thus widens representable color space, has been proposed. This technique limits the minimum value (under color) of the multilevel yellow, magenta and cyan components in one pixel, based on multilevel yellow, magenta, cyan data, and limits an ink-discharge amount of a primary color represented by a single ink color (any of yellow, magenta, cyan), or an ink-discharge amount of a secondary color represented by combination of two primary colors such as yellow and magenta, cyan and yellow, and magenta and cyan.
Conventionally, the above ink-jet printing method performs desirable density control to adjust each ink-discharge amount for multilevel yellow, magenta, cyan and black colors. The density control increases or decreases density of each color.
However, as a conventional density control is made by simply increasing or decreasing density of each color ink, in the above processing to limit respective ink-discharge amounts for allowing discharge of respective color ink within limitation of ink-discharge amount with respect to a print medium, if the density control is performed on multilevel data, under the limitation of ink-discharge amount, to increase the ink density, the ink of an amount exceeding the allowable ink-discharge amount with respect to the print medium is discharged as a result of the density control.
Further, in the ink-jet printing method, density control corresponding to each ink-discharge amount of each color ink is performed by each of multilevel cyan (C), magenta (M), yellow (Y) and black (K) color components, which disturbs gray balance.
In a low-cost color printer which mainly performs printing by using C, M and Y three color ink, a gray color is represented by overlaying the C, M and Y ink droplets. In this printer, if density control is performed by increasing or decreasing each color density, gray balance is disturbed. For example, if cyan density is increased, the resulted gray has a bluish tint.